Grinding wheel dressing



Jan. 23, 1945. J FINDLATER 2,367,857

GRINDING WHEEL DRESSING Filed Dec. 31, 1942 H5 5 INVENTOR.

UAQK H. ENDLATER BY% W Patcnied Jan. 1945 GRINDING WHEEL nan-same JackH. Flndlater,

Packard Motor Car Company, a corporation of Michigan Detroit, Mich minorto- Detroit, Mich Application December 31,1942, Serial No. 470,726

3 Claims.

This invention relates to the dressing of grinding wheels andparticularly to such dressing by the use of a diamond cutting tool.

The invention will be described in connection with a grinding wheelhaving a peripheral crosssection of V-shape, with the side facesof the vstraight or in a right line, but the invention may be adapted todressing wheels of other contours and is not intended to be limited tothe specific form shown other than as indicated in the claims. Such agrinding wheel as is illustrated may be used for grinding threads,external or internal, but it may be used for other purposes and itscross-sectional form may be changed to. suit its particular purpose.

One of the purposes of grinding threads instead of cutting orrollingthem is to obtain extreme accuracy, smoothness, and uniformity, and inthe use of a grinding wheel for the purpose the wheel itself must bemaintained so that its abrading surfaces are always in as nearly exactshape and relationship as it is possible to keep them. In practice,therefore, these abrading surfaces of the grinding wheel are dressed orrenewed at frequent intervals to maintain this accuracy, and sometimesthis dressing is done as aften as between every grinding operation.

Grinding wheel dressing of the character described is in practice mostfrequently accomplished with a diamond crystal set, in a holder to forma tool and this tool is mounted on a support and moved across the faceof the grinding wheel as the latter is rapidly rotated on its axis. Thediamond crystal is set with a 'sharp point extending from its holder andthis sharp point is advanced to contact with the wheel face to bedressed. The tool is then moved across the face of the wheel.

For the particular type of grinding wheel dressing referred to herein,diamond crystals of octahedron shape are usually selected and mostgenerally these diamonds are somewhat elongated so that their-twoprincipal opposite points are farther apart than the greatest diameterat the middle. In using such a diamond about one-half of it is imbeddedin the material of the holder so that one of the sharp points extendsabove the holder and when that point is worn down by use the diamond isremoved from the holder and reversed so that the opposite point isuppermost and the worn point is imbedded in the material of the holder.Thus each octahedron diamond crystal has two working points and whenboth are dulled .the diamond is discarded or given over to other uses.

It is well known that diamonds of natural formation have a hard skin ofappreciable thickness, which is doubtless the reason for selectingdiamonds .of natural octahedron shape for wheel dressing such asabove-described instead of using diamonds of other shapes and lappingthem to a point. A diamond cut or lapped to shape has had its hard skinremoved and consequently it will not wear as well as a natural diamond.Also, by selecting diamonds that are pointed in their natural state thecost involved in the lapping opereration is saved.

It is one of the objects of the present invention to greatly increasethe diamond life in a grinding wheel dressing operation such asreferredto herein.

Another object of the invention is to greatly increase the number ofuseful cutting points on an octahedron diamond for use in dressinggrinding wheels.

Another object of the invention is to provide a four-pointed diamondtool for dressing grindwhich the octahedron ural point lapped of! toform a four-point cuting machine is indicated at ing wheels andparticularly the provision of such a tool in which the points are formedby the hardest portlon of the diamond.

Referring to the drawing,

Fig. 1 is a side view oi a portiorfof a grinding wheel and dresserembodying the invention;

Fig. 2 is a plan view of the grinding wheel and dressing tool;

Fig. 3 shows a dressing tool having the usual octahedron diamond; v

Fig. 4 shows a dressing tool of this invention in diamondhas had itsnatting tool;

Fig. 5 is a still greater enlarged view of the end of a dressing toolindicating how the diamond may be lapped to provide the multiple cuttingpoints.

Fig. 6 shows a diamond that has been lapped off at both ends; and

Fig. '7 is an end view of a diamond showing the four cutting points.

For better illustration the diamond in each of the figures referred tois considerably enlarged.

In the drawing the grinding wheel of the dress- W, the dressing tool ismarked T, and the diamond is marked D. No attempt has been made to holdthese parts to proper relative sizes because to make the diamond assmall as it is used in practice would 4 make it extremely difllcult toillustrate. Thus, the grinding wheel may be three or four inches or afoot in diameter, depending upon the character of work it is to do, andusually the diamond is no more than one-half carat and probably does notextend above the surface of its holder more than a sixteenth of an inch.

The grinding wheel W is mounted on a suitable part of the machine at Hor other suitable means. The sectional form of its cutting periphery isshown in cross section at l2 in Fig. 1 and in plan at IS in Fig. 2. Asshown, the cutting part of the wheel is V-shapecl with straight sidefaces l4 and the shape of the side faces determines the shape of thethread to be out. As the point of the V is worn the wheel must bedressed to reshape the point, and this is done by passing a diamonddressing tool across the face of the wheel in a plane parallel with ortangent to that face. There are usually two of these tools working inunison, one on either side of the wheel, but for the purpose ofillustrating ,the invention only one such dressing tool is shown. Itwill be understood that a similar tool may simultaneously traverse theface M of the wheel on the other side thereof.

A means for moving the dressing tool across the face of the wheel andparallel thereto is shown in Fig. 1, this means comprising a framehaving a slide 2| upon which slides a support 22 for the cylindricaltool T, adjustably held therein by the bolt 34. Said support is movedalong the sliding surface by an arm 23 suitably operated by the machine.The slide 2| is arranged at the correct angle to move the tool in thedesired plane relative to the face ll of the grinding wheel. In Fig.2this plane of movement is indicated by the broken line X.

In Fig. 3 there is shown the conventional diamond tool comprising aholder 25 having a diamond D of octahedron shape imbedded in the softermetal 26 at the end of the holder. Approximately one-half of thediamond-extends above the metal of the holder, this portion of thediamond being of pyramidal shape and the lower half of the diamond be gshown in dotted lines indicating that the lower half also is ofpyramidal shape, these two pyramids being base-to-bas'e and therebyforming the ordinary octahedral crystal. The sharp point 21 of thediamond is what is usually employed to trim the sides of a grindingwheel, and when that point is worn down until it is no longer useful,the diamond is removed from the holder, as by melting the soft metal 26,is then reversed in the holder so that the dull point is below thesurface and the newer, sharpened point is exposed. The tool is then useduntil this second point of the diamond crystal is dull, and then thediamond is supposed to be of no further value for dressing purposes.

This applicant, however, has found that an octahedron diamond such asreferred to above can be made to provide additional hard cutting pointsafter the first cutting point has been dulled. This is accomplished bylapping off the point of the pyramid projecting from the holder so thata square, flat top 32 is formed on the diamond, as shown in Figs. 4, 6and '7. This provides four points 30, one at each corner of the square,and each point, as shown within the circle 33, is formed by two hardnatural sides 3| and one lapped face or top 32, But this lapped face 32is edged by the natural skin of the diamond, indicated by the dottedline in Fig. 7, and this skin provides at each of the four points anappreciable depth of hard crystal so that all three sides of each pointare formed by hard skinsurfaces, and since these four points are not asthin as the Ill and is driven by a beltoriginal four-sided point 21there is more body behind the actual cutting part and consequently lessvibration in operating on the grinding wheel. Indeed, it is found inpractice that these threesided points have extremely good cutting andlasting qualities and when properly presented to the side face of agrinding. wheel they will dress the wheel with an even greater degree ofaccuracy than the original point 21.

In use, one of these points 30 is first presented to the side face ofthe grinding wheel for the dressing operation and used until dulled;then the diamond tool is turned approximately to present another of thepoints 36. Thus the tool may be turned successively to its four pointpositions and when all four points have been dulled with use, thediamond is removed and reversed and the pyramid of the other'end of thediamond is used as was the first half thereof. With this tool, insteadof having only two useful cutting points each octahedron diamond has tenuseful points, the original single point at each end and the four pointsat each end provided by lapping the diamond to form the squared flattop. A diamond that has had both ends lapped oil. is shown in Fig. 6.

Indeed, in some instances each pyramid end of the diamond may be lappedtwice or more as shown in dotted lines in Fig. 5. Here the point 2'! maybe used until dulled, then the diamond may be lapped to a flat top asshown in dotted lines at 28, and after the four points of that squarehave been dulled the diamond may be again lapped to present a four-pointsquare as shown by the dotted lines 29 in Fig. 5. Thus, that pyramidhalf of the diamond has provided nine useful cutting points before thediamond is reversed in the holder. The number of times the diamond canbe lapped oif depends, of course, very largely upon the size and shapeof the crystal itself. In practice some diamonds have been lapped off asmany as four times on one end, thus providing seventeen dressing pointsinstead of one.

In Figs. 1 and 2 is shown the position of the diamond tool with relationto the grinding wheel. The-four points 30 of the tool may beconsecutively presented to the face of the grinding wheel by merelyturning the tool T 90 on its axis and the wheel in this instance beingmounted on a horizontal axis for rotation in a vertical plane. The termhorizontal and vertical are used in the specification and claims toillustrate the relative positions of the parts.

As shown, the axis of the tool T is set at an angle of about 45 from theplane of rotation of the grinding wheel, and with a grinding wheelpointed 55 the angle between the face thereof and the axis of the toolwill be 72%. Also, the tool is arranged in its support so that two ofthe side edges of the diamond are in a horizontal Thus the two sidefaces of the diamond nearest the face of the grinding wheel will formtwo of the three. sides of the cutting point and these two sides are thenatural hard sides of the diamond crystal and consequently give thecutting point maximum hardness.

While I have herein described in some detail a specific embodiment of myinvention, which I deem to be new and advantageous and may specificallyclaim, I do not desire it to be understood that my invention is limitedto the exact details of theconstruction, as it will be apparent thatchanges may be madetherein without departing from the spirit or scope ofmy invention.

What is claimed is:

1. A wheel dressing diamond comprising a crystal having a portionthereof of pyramid shape with the point removed leaving a flat faceforming a plurality of cutting points the side faces of the pyramidhaving natural skin surfaces.

2. A wheel dressing diamond comprising a crystal, a portion of which isof rectangular pyramid shape with the point of the pyramid removedleaving a square face normal to the major axis of the crystal andforming cutting points, each cutting point having three sides and formedfor an appreciable depth of the hard natural skin of the crystal.

3. A wheel dressing diamond comprising a diamond having a portionthereof of rectangular pyramid shape with the point of the pyramidremoved leaving a square flat face forming four cutting points, the fourside faces of the pyramid having natural skin surfaces.

JACK H. FINDLA'I'ER;

